XFM.si
The AI guide to FM radio: how broadcasting actually works
Frequency modulation, transmitters, antennas, and a century of radio history - explained clearly. XFM.si is an independent educational resource about FM radio technology and is not affiliated with any radio station, network, or broadcaster.
No card required · $9/mo Plus · $99/mo Premium
What you get
Everything XFM.si gives you
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FM physics explained
Frequency modulation, bandwidth, and signal theory in plain language.
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Radio history timeline
From Edwin Armstrong's 1933 invention to today's digital and streaming radio.
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Broadcast engineering basics
Transmitters, power classes, antennas, and effective radiated power.
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Industry today
Licensing, HD Radio, and how streaming has reshaped broadcast radio.
Go deeper
Radio Knowledge Base
Explore the science, history, and engineering behind FM broadcasting.
FM Radio History
- Edwin Armstrong's invention — Armstrong demonstrated wide-band FM in 1933, solving AM's static problem.
- First FM broadcasts — Experimental FM stations launched in the late 1930s in the United States.
- FM stereo standard — The FCC approved FM stereo broadcasting in 1961, transforming music radio.
- AM-to-FM shift — By the 1970s-80s, FM overtook AM as the dominant music radio band.
Broadcast Engineering
- Modulation basics — FM encodes audio by varying carrier wave frequency rather than amplitude.
- Channel spacing — US FM channels are spaced 200 kHz apart across the 88-108 MHz band.
- Transmitter power classes — Stations range from low-power community signals to high-power regional ones.
- Antenna and ERP — Antenna height and effective radiated power determine a station's coverage area.
Radio Industry Today
- Licensing bodies — National regulators like the FCC (US) or Ofcom (UK) assign and license frequencies.
- HD Radio — A digital-analog hybrid system adding extra channels and clearer audio.
- Internet and streaming radio — Streaming has added new competition and new distribution for traditional stations.
- Format changes — Stations often change music formats and branding while keeping the same frequency.
Pricing
Simple plans that grow with you
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Plus
$9/mo
- ✓200 questions per day
- ✓Full saved conversation history
- ✓Deep dives on broadcast engineering topics
Premium
$99/mo
- ✓Unlimited questions
- ✓Extended deep-dive answers
- ✓Everything in Plus